Low-lying states in {sup 32}Mg studied by proton inelastic scattering

Proton inelastic scattering on the neutron-rich nucleus {sup 32}Mg has been studied at 46.5 MeV/nucleon in inverse kinematics. Populated states were identified by measuring de-excitation {gamma} rays, in which five new states were found by {gamma}-{gamma} coincidence analyses. By analyzing the angular differential cross sections via coupled-channel calculations, their spins and parities were constrained and the amplitudes for each transition were extracted. The spin and parity of the 2321-keV state was assigned as 4{sub 1}{sup +}. The ratio between the energies of the 2{sub 1}{sup +} and 4{sub 1}{sup +} states indicates that {sup 32}Mg is a transitional nucleus rather than an axially deformed rigid rotor. The collectivities in the nucleus {sup 32}Mg with N=20 are discussed based on the results obtained in the present experiment.

[1]  S. Takeuchi,et al.  The first excited state of 30Ne studied by proton inelastic scattering in reversed kinematics , 2003 .

[2]  R. Varner,et al.  A global nucleon optical model potential , 1991 .

[3]  S. Shimoura,et al.  Liquid hydrogen and helium targets for radioisotope beams at RIKEN , 2005 .

[4]  S. Takeuchi,et al.  Deformation of 34Mg studied via in-beam γ-ray spectroscopy using radioactive-ion projectile fragmentation , 2001 .

[5]  J. Sida,et al.  Electric and nuclear transition strength in 30,32Mg , 2001 .

[6]  H. Sagawa,et al.  Low-lying intruder 1− state in 12Be and the melting of the N=8 shell closure , 2000 .

[7]  F. Touchard,et al.  β-Decay schemes of very neutron-rich sodium isotopes and their descendants , 1984 .

[8]  V. A. Madsen,et al.  Neutron and proton transition matrix elements and inelastic hadron scattering , 1981 .

[9]  T. Teranishi,et al.  Isomeric 0+ state in 12Be , 2001 .

[10]  P. Fallon,et al.  Transition to the Island of Inversion: Study of Excited States in 28-30Ne , 2006 .

[11]  Brown,et al.  Mass systematics for A=29-44 nuclei: The deformed A~32 region. , 1990, Physical review. C, Nuclear physics.

[12]  J. Duprat,et al.  In-beam gamma spectroscopy of very neutron-rich nuclei at GANIL , 2008 .

[13]  R. Ronningen,et al.  Role of intruder configurations in Ne and Mg , 1999 .

[14]  J. Berger,et al.  Evolution of the N = 20 and N = 28 shell closures in neutron-rich nuclei , 2000 .

[15]  Toshio Suzuki,et al.  Nuclear radii of Na and Mg isotopes , 1998 .

[16]  Wagner,et al.  Direct evidence for the breakdown of the N = 8 shell closure in 12Be , 2000, Physical review letters.

[17]  T. Nakamura,et al.  Development of large deformation in 62Cr. , 2009, Physical review letters.

[18]  W. Mittig,et al.  Shape coexistence and the N = 20 shell closure far from stability by inelastic scattering , 2002 .

[19]  M. Taylor,et al.  Probing shell structure in neutron-rich nuclei with in-beam γ-spectroscopy , 2002 .

[20]  Brown,et al.  Proton inelastic scattering on 56Ni in inverse kinematics. , 1993, Physical review letters.

[21]  T. Otsuka,et al.  Varying shell gap and deformation inN∼20unstable nuclei studied by the Monte Carlo shell model , 1999 .

[22]  Arjan J. Koning,et al.  Local and global nucleon optical models from 1 keV to 200 MeV , 2003 .

[23]  I. Tanihata,et al.  Delay-line PPAC for high-energy light ions , 2001 .

[24]  T. Otsuka,et al.  Vanishing of the shell gap in N = 20 neutron-rich nuclei , 1992 .

[25]  T. Kubo,et al.  Neutron-dominant quadrupole collective motion in C16 , 2006 .

[26]  John W. Negele,et al.  The Structure of Finite Nuclei in the Local Density Approximation. , 1969 .

[27]  R. Janssens,et al.  Measurement of E2 transition strengths in {sup 32,34}Mg , 2005 .

[28]  A. Poves,et al.  The onset of deformation at the N = 20 neutron shell closure far from stability , 1987 .

[29]  Isao Tanihata,et al.  The RIKEN radioactive beam facility , 1992 .

[30]  D. Guillemaud-Mueller.  Spectroscopy of nuclei far from stability at GANIL: Recent experiments , 2002 .

[31]  A. Yoshida,et al.  Prototype of superferric quadrupole magnets for the BigRIPS separator at RIKEN , 2004, IEEE Transactions on Applied Superconductivity.

[32]  T. Kubo,et al.  Large collectivity of 34Mg , 2001 .

[33]  André Lejeune,et al.  Optical-model potential in finite nuclei from Reid's hard core interaction , 1977 .

[34]  S. Shimoura,et al.  Large deformation of the very neutron-rich nucleus 32Mg from intermediate-energy Coulomb excitation , 1995 .

[35]  Takashi S. Nakamura,et al.  Quadrupole deformation of 12Be studied by proton inelastic scattering , 2000 .

[36]  Bazin,et al.  Decay properties of exotic N , 1993, Physical review. C, Nuclear physics.

[37]  B. A. Brown,et al.  Thick-target inverse-kinematics proton scattering from Ar 46 and the N = 28 shell below Ca 48 , 2005 .

[38]  T. Kibédi,et al.  REDUCED ELECTRIC-OCTUPOLE TRANSITION PROBABILITIES, B(E3;01+→31−)—AN UPDATE , 2002 .

[39]  F. Nowacki,et al.  Shell model study of the neutron rich isotopes from oxygen to silicon , 1998 .

[40]  Steiner,et al.  New Region of Deformation: The Neutron-Rich Sulfur Isotopes. , 1996, Physical review letters.

[41]  T. Otsuka,et al.  Nuclear mean field on and near the drip lines , 1996 .

[42]  Suzuki,et al.  New magic number, N = 16, near the neutron drip line , 2000, Physical review letters.

[43]  L. K. Fifield,et al.  Decay properties of exotic [ital N][congruent]28 S and Cl nuclei and the [sup 48]Ca/[sup 46]Ca abundance ratio , 1993 .

[44]  Y. Blumenfeld,et al.  Proton scattering by short lived sulfur isotopes , 1999 .

[45]  Shape coexistence and the effective nucleon-nucleon interaction , 1999, nucl-th/9903037.

[46]  B. A. Brown,et al.  Quadrupole collectivity in silicon isotopes approaching neutron number N = 28 , 2007 .